1. Field of the Invention
The invention relates to a device for emptying bulk material from silos, having a clearing device which removes the bulk material on the upper surface of the bulk material heap, can be lifted and lowered in the silo and feeds the bulk material to a telescopic fall pipe which extends vertically through the silo and is coupled to the clearing device such that it follows the lifting movements of the clearing device by telescope-like retraction and extension, with the telescopic fall pipe having an upper coupling pipe with a bulk material inlet and coupled to the clearing device, and at least one sliding pipe adjoining the inlet downwards towards the silo base.
2. Description of the Related Art
In small silos, which are used for accommodating silage, it is known to provide as a delivery shaft for the stored material a self-supporting telescopic fall pipe which is arranged centrally in the silo, the upper pipe of which bears a clearing arm, pivotable about the silo axis, and is provided with an inlet for the stored material conveyed by the clearing arm (German Auglegeschrift No. 1,250,360). At the same time, the upper pipe forms a coupling pipe with which the retracted telescopic fall pipe, together with the clearing unit, is pulled back upwards in the silo by means of a winch rope.
In another known silo-emptying device which is intended for isolated small silos for accommodating lumps of ice, a telescopic fall pipe is also used as the delivery shaft, which telescopic fall pipe, however, in this device, leads with its individual pipes to an internal, fixed stand pipe (German Patent Specification No. 831,519). As a result of the stand pipe, the conveying cross-section of the telescopic fall pipe is narrowed and at the same time the expense of construction is increased.
The known silos having a central delivery shaft designed as a telescopic fall pipe have not been able to become established in practice for bulk material silos of larger storage capacities. A difficult problem with these devices is that the telescopic movements of the telescopic fall pipe standing in the stored material cannot be reliably controlled in use. When the clearing unit is lowered in the silo, the telescopic fall pipe is certainly forced to retract, but at the same time it is unable to reliably retract gradually section by section from the bottom upwards. On the contrary, the individual pipes of the telescopic columm or even entire groups of pipes of the same can prematurely retract in an uncontrolled manner before the pipes lying underneath are retracted. The consequence of this is that the pipes or pipe groups which have been prematurely retracted, as soon as the adhesive force at the surrounding bulk material is overcome, fall down suddenly in the telescopic column under their own weight before they hit the flange of the pipe section lying underneath. This uncontrolled falling of individual pipes or even entire pipe groups, with the considerable weight of the same, leads to exceptionally high shock loads and, as a consequence thereof, to severe vibration and serious damage to the entire installation. Repairing the telescopic fall pipe standing in the stored material is exceptionally laborious and time-consuming.
Of course, the abovementioned problems occur to a considerable extent if bulk materials which are not reliably free-flowing are stored in the silo, for example such bulk materials as gypsum, saline manure or other salts, and bulk materials comparable in behaviour, which tend to stick, compact or even harden. No bulk-material clearing and discharge devices are as yet available which are absolutely reliable for the storage of such difficult bulk materials in large silos.